In several communications systems the data to be transmitted is compressed so that the available bandwidth is used more efficiently. For example, the Moving Pictures Experts Group (MPEG) has promulgated several standards relating to digital data delivery systems. The first, known as MPEG-1 refers to ISO/IEC standards 11172 and is incorporated herein by reference. The second, known as MPEG-2, refers to ISO/IEC standards 13818 and is incorporated herein by reference. A compressed digital video system is described in the Advanced Television Systems Committee (ATSC) digital television standard document A/53, and is incorporated herein by reference.
The above-referenced standards describe data processing and manipulation techniques that are well suited to the compression and delivery of video, audio and other information using fixed or variable length digital communications systems. In particular, the above-referenced standards, and other "MPEG-like" standards and techniques, compress, illustratively, video information using intra-frame coding techniques (such as run-length coding, Huffman coding and the like) and inter-frame coding techniques (such as forward and backward predictive coding, motion compensation and the like). Specifically, in the case of video processing systems, MPEG and MPEG-like video processing systems are characterized by prediction-based compression encoding of video frames with or without intra- and/or inter-frame motion compensation encoding.
It is often necessary to convert 24 progressive frames per second (fps) video material, such as film, to a 30 interlaced frames per second (60 fields per second) video format, such as the NTSC format. This conversion is accomplished using the well-known 3:2 pull-down technique, where the top and bottom fields of the progressive film materials are alternately repeated for alternate frames to obtain 10 fields from 4 progressive frames (i.e., 60 fields from 24 frames). The sequence of fields produced using the 3:2 pull-down technique is as follows (where T stands for top and B stands for bottom field): T0, B0, T9, B1, T1, B2, T2, B2, T3, B3, T4, B4, T4 . . . .
In an MPEG-like encoder it is desirable to determine if the video material being encoded has been processed using the 3:2 pull-down technique, since the repeated fields can then be removed so that only the original 24 fps material is encoded (as progressive frames). The pull-down information can be passed on to the decoder using MPEG-2 compliant flags. In the absence of such detection, the repeated fields are coded again resulting in up to 20% loss in the performance or compression. Unfortunately, present 3:2 pull-down detectors require an inordinate amount of processing and memory resources. Moreover, due to, e.g., transcoding errors generated during the 3:2 pull-down processing of a video signal, present 3:2 pull-down detectors frequently produce "false detections," which negatively impact subsequent encoding of the video signal.
MPEG-2 encoders utilizing the TM-5 recommended rate control algorithm typically do not properly encode a "mixed mode" video signal, i.e., a video signal including material processed by the 3:2 pull-down technique and original 30fps or 60fps material. In such a case (even with flawless 3:2 pull-down detection), the MPEG-2 encoder will, at best, inefficiently encode the 3:2 pull-down processed material.
Therefore, it is seen to be desirable to address the above-described problems by providing a method and concomitant apparatus for adapting and enhancing the behavior of an MPEG-like encoder to the presence and/or absence of 3:2 pull-down processed video information within a video information stream to be encoded. Moreover, it is seen to be desirable to provide a robust and computationally efficient method and concomitant apparatus to determine if a video information stream to be encoded has been subjected to 3:2 pull-down processing.